Seeds of Woody Plants
Collecting,Cleaning, Shipping. The studies of seeds ofplants, their collection, care and requirements for germination, has been an intriguing one over the years. Mouth work has been done,mostly with the seeds of cereals, annuals and trees used for reforestation. Textbooks on forestry have much detailed information forest tree seeds, but the seeds of many woody ornamental plants have not been studied as thoroughly as many a commercial grower would wish.
Collecting
Seeds should not be collected until they are ripe, for in many cases seeds collected pre-maturely do not germinate. Any collector who has had experience in this field knows that there are various methods of determining the ripeness of the fruit—the shriveling of the pod or the cord connecting the seed to the pod in the legumes, the color or softness of the pulp of the fruit of Malta, Vibrant and Cotoneaster, and close examination of the cones of coniferous trees, sometimes even tested by determining the specific gravity of the unopened cones.
Seeds should be collected wherever possible from pure stands. There are many groups of plants which cross-pollinate easily, and when seed is collected from arboretums or other closely planted collections of many species,there is ample opportunity for hybridization.This is also true in nature, to that in order to insure good seed, collect it either in pure stands or from isolated specimens.
One very important fact to keep in mind is that the seed of many, a variety, botanical as well as horticultural, may not “come true to name.” There are some cases, admittedly, in which the variety will yield a surprising percentage of the seedlings true to name. Such is the case with Uterus rebury Fastigiate’. But the rule in most cases is that the seed of the variety yields seedlings similar to the species.
The actual date on which seed ripens in one locality may vary from year to year in the same way and for the same reasons as do the blooming dates of plants and the autumn color.ften one makes a special effort to collect seed of a certain plant only to find, on coming to the plant, that all the seed has fallen on the ground or been eaten by the birds and rodents, or has been partially destroyed by weevils. The seeds of witch-hazels, in particular, must be collected before the capsules open, for at that time the yare actually thrown considerable distances by the explosive opening of the capsule. Certain plants like China Virginias, with fleshy fruits, may appear ripe one day and be gone the next, merely because a flock of birds has taken them all from the plant in a few hours’ time.here are many plants which retain their fruits for a long time in the fall, and far into the winter, and these may be collected over a long period. Many of the seeds collected on the date sin the following list will need to be cleaned and dried, preferably in the greenhouse. Then there is an after-ripening period, or a period of dormancy, for many seeds so that frequently it is months from the time the seed is collected before it is ready for planting. However, when seed is to be obtained for special purposes, it is best to collect it as soon as it is ripe, instead of waiting and taking the chance of its disappear-in. The following list of dates on which seed collections have been made in the Arnold Arboretum in Boston, Mass., can be consider-ably more flexible than the single date entry would lead one to believe. All these dates should be coordinated with the fruit ripening dates in the locality where the list is to be used,and collecting dates for many more can be inserted as they become known.
Cleaning Seeds
Most seeds must be cleaned before they are sown. The fruits of osseous plants, vinculums,magnolias, dogwoods and many other fruits with pulp about the seeds, must be cleaned before the seed is shipped or even before it is stored in large quantities, for the rotting pulp quickly heats and in many cases the high temperatures will kill the embryos. Even elm seed toast be dried before it is shipped. This seed is frequently picked while it is still slightly green on the tree, or picked up from the ground while it is damp, and if stored or shipped in large quantities before it is thoroughly dry, it may heat and be completely killed on arrival.On the other hand, many of the seeds pro-duce in dry capsules, like those of the crustaceous plants, spire as, mock oranges, etc.,can be merely sun-dried and then shipped.here are many ingenious methods for cleaning seeds, some of them worked out on the spur of the moment. Cones from evergreen and cone-bearing deciduous trees must be dried an din many cases have hot air applied to them in order for the cones to open and allow the seeds to fall out. For a few cones, this is easily accomplished in the hot sun or on the greenhouse bench, with the cones on screens so that the seed will fall into a receptacle below. For large quantities of cones, the foresters have is vented several typos of drying kilns.
Conifer seeds and others such as maple an dash, can be shipped with the wings on, but should be de winged before they are sown. This can be accomplished in several ways, but for small amounts the best method is by han drubbing; or, secondly, by lightly rubbing the seeds over a screen. Too much pressure can injure the seeds, so care must be taken in this operation. Screening and even fanning of the resultant mixture are means of separating chatter seed.
Some of the larger seed can be handled by regular farm machinery. Hulls of the Black Walnut, for instance, can be removed by running the fruits through the corn sheller. Various fruits can be run through threshing equipment in order to produce clean seed.
Finally, the pulpy seeds are usually cleaned by macerating them and soaking them in water during which process the pulp and poor seeds usually float to the surface and can be removed, while the viable seeds sink and can be dried later for storage and shipping. Acorn shave been “cleaned” by the water method, since the cups and weevil acorns float and the viable acorns sink to the bottom. Naturally, the amount of seed to be cleaned governs the method chosen.
For small amounts of seed the Wrangled is most serviceable. This has been used by several institutions (and possibly similar blenders have been used, as well). One should remove the metal blade of this electrically operated, household machine and substitute one cut from the casing of an automobile tire.This is a small piece of rubber 1 1/2 in. square held horizontally on the revolving axis of the machine. The standard whirling metal blade which comes with the machine will quickly scarify and injure the seeds of many plants and hence should not be used. Even with the rubber blade, the fruits should be completely ripe to that the flesh is easily macerated (or else it should be partly macerated in advance by hand)and the seed put in for no longer than 5 minutes,together with an ample supply of water.The length of time depends on the kind of seed,its degree of softness and the amount of seed.None larger than the fruits of Prunes americana or P. hotelman should be used. Obviously, only small amounts of seed can be handled in this fashion, but undoubtedly larger equipment could be made if necessary. This method has proved a timely and quick one for cleaning small amounts of pulpy seed.
Many seeds are sun-dried after the cleaning process and then sown, stratified or stored, but if one wants to be certain no disease gets into the seed, a simple treatment with some disinfectant, such as washing in a 5-10% solution of potassium permanganate might be well worth the effort. To kill weevils and worms and other insects, the seeds may be dusted with rotenone, available in most countries. With acorns, carbon bisulfide has been used to kill theweevils. A small amount is placed in a largecovered container and the acorns left in longenough to kill the weevils. Naturally the amountof the chemical used depends on the size of thecontainer and the amount of seed to be dis-infected. The use of this chemical may notprove suitable for all kinds of seeds.
Shipping Seeds
When seeds must be sent long distances,great care should be taken in their packing andthe means by which they are shipped. Everyseed collector should know something about theseeds he is sending, how they should be cleaned,and which ones should be shipped as soon ascollected. This last point is a very important one.Unfortunately many institutions shipping seedsfrom abroad, and many a botanical collector aswell, consider that all seeds can be handled alike;that is, that they can be stripped from the plantsin the fall, cleaned within a month or to andheld possibly for 6 months until all the seeds areready for shipment at one time or until weatherconditions are such that the collector can takethe time to ship them.
It will be noted from the following lists thatsome seeds cannot be allowed to dry out, butshould be shipped immediately after they arccollected. Certain seeds such as those ofPopulus, Salix, Magnolia and Ulm., shouldalways be shipped promptly by air since theywill remain viable for only a very short time, even under ideal conditions. Willow seeds mayremain viable only a few days.
Seeds of Cytisus, Robinia and Queretts aresusceptible to attacks of weevils or otherinsects and if the period of shipment is long andslow, it may well be that the seed will be worth-less on arrival. Such seeds should be treated withsome material to kill such pests. Carbon bi-sulfide gas has been used satisfactorily withacorns, but the amount used depends on thesize of the closed container in which thefumigating is to be done, the amount of seedand even the kind of seed. One excellent sugges-tion is that such seeds may be dusted with rote-none when they are placed in the packet, theamount of dust used being equivalent to thebulk of the seeds.
Any seeds that might be unusually susceptibleas disease carriers might be treated with amild disinfectant, such as a 5- le/. solution ofpotassium permanganate, then dried andbagged for shipment.
Before the days of air transportation, moistsawdust or moist peat moss could not be used ifthe shipping period were to be lengthy or thetemperatures en route likely to be high, for theseeds would either germinate or the hightemperatures would cause the packing materialsto heat and kill the seeds. To avoid thesedifficulties, seeds were shipped in charcoalwhich, being inert, would not heat or harborfungi, but would absorb a certain amount ofmoisture and so provide a sufficiently moistatmosphere in the package to prevent the seedsfrom drying out.
Today, polyethylene bags can be used toexcellent advantage. Cuttings, scions, budwoodand plants wrapped in this material are sent tomany parts of the world. The polyethylene filmis impermeable to water vapor, but not togaseous vapors. Bags made of polyethyleneshould be tightly sealed, and may containseveral paper packets of seeds and a very smallamount of moistened moss to keep the smallamount of air in the bags slightly humid, forthose seeds which should not dry out. Anothermethod for shipping such seeds as acorns orchestnuts would be to dip them in paraffin.The plant quarantine laws of the UnitedStates prohibit the entry of certain seeds intothis country. None can be sent in with moistpulp about them. In the northern part of theUnited States, the more important woodyplants the seeds of which are prohibited areBerberis species, Ribes nigrum and bamboos andtheir relatives. These same quarantine lawsapprove only certain packing materials, suchas peat moss, sphagnum, excelsior, woodshavings, sawdust, ground cork, buckwheathulls, expanded vermiculite and charcoal.
Prohibited packing materials are soil, sand,leaves, forest litter, woods moss, hay, straw,etc.—anything taken from direct contact withthe soil. Seeds packed in such materials will beprohibited entry.
Seeds of woody plants collected in foreigncountries and destined for recipients in theUnited States must be accompanied by apermit. The Bureau of Entomology and PlantQuarantine of the U.S. Department of Agricul-ture issues such permits to individuals andinstitutions upon application. A number isgiven the applicant and this number appears ona standard green and yellow tag bearing theaddress of the quarantine station (Hoboken,NJ., Miami, Fla., Laredo, Tex., or SanFrancisco, Calif.). This required tag is the onlyaddress appearing on the outside of the package,other than the collector’s name and address inthe upper left-hand corner.The following 3 lists do not contain all thosewoody plants commonly grown from seed, butthey should serve as a guide to collectors toindicate how certain seeds should be handledand how rapidly they should be shipped. Special emphasis should be placed on list “A” as the”perishable” group. List “B” includes thosewhich can be sown or stratified at once or driedand used later. List “C” contains those which.n be kept in a dry condition, some of themfor periods longer than I year.
The procedure in shipping seeds shouldtherefore be:
1. Clean all seeds thoroughly and at once,taking special precautions not to allowpulpy or wet seeds to “heat” beforecleaning.
2.Prevent certain seeds from drying out‚ÄîList “A”‚Äîby proper packaging.
3.Properly dry the remainder.
4.Fumigate or in other ways treat forinsects or disease pests if necessary.
5.Label all seed packets completely.
6.Ship as soon as picked (and by air) thosein List “A.”
7.Send the remainder of the shipment assoon as possible, keeping the seeds dryand away from contamination with insectand disease pests.
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